The Eastern Kingdoms are home to some of the most industrialised places on Azeroth and have seen bustling long-term civilisations for thousands of years.

The Scourge live in Northrend. Despite all of the efforts of the WotLK expansion they seem still fairly strong.

Kalimdor has lots of resources and some tough races..

Then finally Pandaria has peace-loving hippies (Pandaren), a broken collective of clans of a once-great people (Mogu), and one recently-shattered major power (Mantid).

I see a bias there.

The Scourge is actually being contained and prevented from raising new units by Bolvar, he's not actively out to dominate the world like his predecessors.

If you call them a threat, you're going on X.0 instead of the present status. Thereby Pandaria should count the Mogu and Mantid as threats.

"Oh, who does my hair? You might have heard of my stylist. It's called the Void!"
"No matter how much you plead I will not sprout tentacles or turn into a giant eyeball. Well, I might. But not because you asked!"

Pandaria. The Swarms of the Mantid and the endless construct armies of the Mogu, alongside the Shado Pan, with some extra help from the Yak/Tauren things i somehow forget their names at this moment, the Jin'yu, and Hozen. You can even argue that you could include the Zandalari in this argument as they seem to have their base of power set in Pandaria. Mantid numbers, Mogu brutality, Zandalari cunning, and all of the Pandaren groups seems pretty powerful.

That above pretty much sums up why Pandaria is so dominating. For Northrend, there's one massive game changer; The Lich King. Basically every death from any of the other sides is one more warrior for the Northrend faction. Add to the sheer overwhelming numbers, survivability, and staying power of an undead the numbers of Dragons, Dragon Aspects, Frost Giants, and Titan constructs, and you have a major power to contend with. For the dragons, you have the Red and Blue dragon flights based out of Northrend. Another group, the Kirin Tor, the worlds most powerful mages. Assuming they don't retreat back to their homelands, their contributions would be astronomical. They could open portals for surprise attacks anywhere in the world.

Some really good points being brought up in this thread. But a few things to remember before you count out Kalimdor and Pandaria...

Pandaria is inhabited by the Mogu and there is perhaps no better counter to the Scourge than the spiritbinding magics of the Mogu. After all, stone isn't alive, so it can't be risen into undeath.

Kalimdor while not industrialized, and somewhat primitive by the standards of other continents, is home to the vast majority of Azeroth's Druids. Not only that, but the Ancients themselves have recently returned to Kalimdor. Something to consider at least.

Bolvar could just resurrect Galakrond (seriously Arthas should have just done that himself instead of sending that necromancer...) and wipe everyone else off the map. And that's not even going into the armies of the Keepers, Nerubians, Drakkari, Wyrmrest Accord, Ebon Blade, Kirin Tor, Vrykul/Kvaldir. The only real competition would be Pandaria, and they don't really have a faction to oppose the Scourge.

Q: Where the fuck is Xia Xia, SIU?!?!
A1: She needs to start making eggs for Easter...
A2: Drunk and sleeping somewhere.

I voted Kalimdor. The night elves dealt with the Mantid cousins in Silithus, they could do it again with those in Pandaria.

My only concern is that Eastern Kingdoms contains most of the tacticians of both factions in game, so while Kalimdor is much easier to defend than Eastern Kingdoms (imo) i'm sure they would find a way in.

Eastern Kingdoms have the greatest combination of brute strength and magic. Humans, Blood Elves, Forsaken and Gnomes make up the large majority of magic users across all 4 continents. Human, Dwarves and Forsaken also have the armies build for large scale war and the only possible match ups to them are Orcs, Scourge and Mantid. Gnomes + BB goblins will provide the best mechanical support in the world. Humans also have the strongest fleet in the world. Other continents are mostly based around a single major power, while everyone else will just provide minor support.

While all continents have their strong points, like The Scourge in Northrend, Thrall/Malfurion in Kalimdor, Plague + Sunwell boosted elves in EK and Mogu/Zandalari in Pandaria, I feel that the two continents with the highest possibility of winning would be Pandaria and Eastern Kingdoms.

Bit more elaborate:

Kalimdor: They have incredible amounts of resources, from the woods of Ashenvale & Feralas to the waters of Thousand Needles, but apart from resources their biggest ace is having Thrall and Malfurion. There aren't many Draenei or Troll around, and Goblins rarely really fight in close combat. Not too sure about Night Elves, but their strongest points are their evasiveness and (used to be) immortality. Outside of their forests I don't see the Night Elves as that big of a threat since they focus too much on guerilla warfare (they hardly wear armor and use Ents instead of catapults/tanks, pretty easily dealt with (FIRE!)). Malfurion and Thrall can wreck some pretty damn serious shit, but army vs. army I don't see the armies of Kalimdor standing up against other continents. Malf and Thrall seem to prefer acting as strategic leaders instead of going out on the battlefield anyway. The Draenei and Trolls are too few in numbers to really pose a threat. The Draenei has a Naaru, but, the Naaru VERY rarely engage in combat because they absorb the darkness around them. It wouldn't end with holy power decimating everything in it's path, it would end like M'uru turning against everyone. The Draenei wouldn't let their Naaru engage in combat at all, I think. The Orcs are strong and plenty, but seem to add about as much to the battlefield as Humans, and that is numbers and numbers only. Apart from having above average strength their forces have no real power (example: Plague) and even if combined with the other races I don't see them being strong enough to survive against the other continents, I'd put it on par with Northrend.

Northrend: The Scourge, the Nerubians, the Vrykul. This continent has some of the bigger threats the world has seen, but apart from Scourge the others could be countered. What is a Vrykul against a Tauren or an Orc anyway? Bigger isn't always better either. To tell the truth I don't know too much about Vrykul and their powers beyond pure strength. Now, Nerubians. In their home environment they would be one of the nastiest races to deal with, being able to make cocoons of people and burrowing underground. But imo they're like the Night Elves and rely too heavily on guerilla warfare, and wouldn't stand that big of a chance above ground. If they stayed in their holes of Azjol Nerub they could hold out for a very long time. But I don't see them winning because of this. The Scourge is one of the major threats in all of this, assuming Bolvar would let them go rampage. They could put out some serious damage, especially to Kalimdor and Eastern Kingdoms, but I don't see this continent prevailing due to the Scourge alone. When they were heavily present in EK and somewhat in Kalimdor (RFD), letting them go rampage would and could give them a win against these continents, but now they're pretty much restricted to Northrend, and have lost some of the major strong points of its army, Val'kyr.

Eastern Kingdoms: Now we're getting there. Dwarven blacksmiths, Gnomish technology, Human numbers, The Sunwell and Elven magic plus the Forsaken with their Plague and Val'kyr. Just like Trolls/Draenei the Worgen aren't that many anymore (Guess that goes for belves too, but they at least have the Sunwell), so there's not much to be said about them. This makes for one of the best combination of races out there. If working together I can see this continent doing VERY well for itself, having the powers of Forsaken Plague, the Sunwell and just lots of numbers with superior technology and armor. Sylvanas strategic mind along with all of this I'd put them above Kalimdor and Northrend. Army vs army Kalimdor doesn't stand a chance. And what's better to counter the oncoming Scourge than other Undead and.. Tirion Fordring, one of the racial/faction leaders that actually goes out on the battlefield to get shit done. The Ashbringer is a major counter against the army of undeath.

Pandaria: The endless forces of Mantid, the Mogu and Zandalari trolls make for what I believe to be the strongest continent. The Mogu are some of the (if not THE) physically strongest races on Azeroth, but as I said before it's not all about pure strength. Their biggest strength against EK/Northrend is their immunity against the plague. They are all about order, are ruthless and strong, AND the undead are nothing against them. Add in the huge trolls of the Zandalari, the goddamn Thunder King who (somehow) solely got the powers of Ra'den, and close to endless numbers of Mantid, with their Paragons having some pretty useful abilities. Pandaria is very alike Kalimdor, but on steroids, and they have better protection against undead forces + Thunder King. *edit* seems like I got it a bit wrong about the undeath part, Mogu are likely to be immune or at least be strong against it. Still counts!

Northrend, maybe Pandaria has powerful races empowered by titanic technology, but Northrend has Yogg-Saron, while Y'Shaarj is known to be very very very dead, so, Northrend wins.

Sure, Y'Shaarj is dead, but Yogg-Saron was defeated. While it isn't dead it sure isn't capable of doing much until it regenerates (otherwise what was the point going in to kick it in the mouth). Right now I wouldn't count in Yogg-Saron's powers.

For the people saying Pandaria, while the Mantid are many, where are the numbers to back up the Mogu, Pandaren and Yangol? EK has a logistical advantage IMO. You can lists races all day long, but if they don't have the man power and/or the tech, you can't say they when due to the those races.